The project is concerned with evaluating the effectiveness of behavioral treatment of young (before the age of 40 months) autistic children. The children are treated in their homes by trained parents and student therapists. Two groups of children are observed: an Intensive Treatment Group (N equals 19) receiving more than 40 hours of 1:1 treatment per week, and a matched group of Less Intensive Treatment (N equals 23) receiving 10 hours or less treatment per week. Final follow-up data will be presented in 1982. The project is also concerned with research in the following areas: (1) Behavioral analysis of perceptual dysfunction ("stimulus overselectivity") in autism and associated problems with shift in stimulus control over behavior; (2) nature and kind of self-controlled sensory and perceptual reinforcers maintaining psychotic (ritualistic and stereotyped) behaviors; (3) effects of mainstreaming (normal peer group influences) on autistic behaviors; (4) development of training procedures for para-professionals (parents, teachers), etc.